This invention relates to an internal combustion engine, and more particularly to an internal combustion engine equipped with an EGR device that recirculates a portion of exhaust gas into an intake passage.
An internal combustion engine is already known that is equipped with an EGR device that has an EGR passage connecting an exhaust passage and an intake passage, and that causes a portion of exhaust gas that flows through an exhaust passage on a downstream side of a turbine to recirculate as EGR gas through the EGR passage to an intake passage on an upstream side of a compressor. A distinction is made between the above-described kind of EGR device and an EGR device that causes a portion of exhaust gas that flows through an exhaust passage on an upstream side of a turbine to recirculate via an EGR passage to an intake passage on a downstream side of a compressor, with the above-described kind of EGR device being referred to as a “low-pressure EGR device”.
According to the low-pressure EGR device, since EGR gas can be recirculated with intake air before pressure-charging, a large amount of EGR gas can be introduced into the internal combustion engine. On the other hand, in a vehicle in which this kind of internal combustion engine is mounted, if a deceleration request is issued while EGR gas is recirculating, there is the possibility that the large amount of EGR gas that was recirculated into the intake passage will cause misfiring of the internal combustion engine. Consequently, various countermeasures with respect to misfiring that is caused by EGR gas during vehicle deceleration are being implemented in internal combustion engines equipped with a low-pressure EGR device. An internal combustion engine in which such a kind of misfire countermeasure is implemented is disclosed, for example, in Patent Literature 1 (Japanese Patent No. 5277351).
The internal combustion engine disclosed in Patent Literature 1 includes: an EGR valve that is provided in an EGR passage; a throttle valve that is provided further on a downstream side than a connecting portion with an EGR passage of an intake passage; a bypass passage that connects an upstream side of the connecting portion in the intake passage with a downstream side of the throttle valve; and a bypass valve that is provided in the bypass passage and that controls the amount of fresh air introduced into a combustion chamber of the internal combustion engine through the bypass passage. According to this system, if it is determined that the aforementioned internal combustion engine is in a decelerating operation state, the aforementioned EGR valve is actuated so as to fully close. Furthermore, if it is determined that the internal combustion engine is misfiring, the aforementioned bypass valve is actuated in a valve-opening direction and the aforementioned throttle valve is actuated in a valve-closing direction.
By actuating the aforementioned EGR valve so as to fully close, the amount of EGR gas that recirculates to the intake passage during vehicle deceleration can be made zero. However, even in a case where the aforementioned EGR valve is actuated so as to fully close, EGR gas that was introduced into the intake passage prior to closing the EGR valve flows into the combustion chamber with a delay relative to the timing of closing the EGR valve, and hence that EGR gas becomes a factor that causes the internal combustion engine to misfire. In this respect, according to the system described in Patent Literature 1, since the bypass valve and the throttle valve operate as described above, the proportion of EGR gas contained in intake gas (a mixed gas of EGR gas and fresh air; the same applies hereunder) that is introduced into the combustion chamber at a time of vehicle deceleration can be reduced. Hence, misfiring of the internal combustion engine that is attributable to EGR gas during vehicle deceleration can be avoided.